1. Field of the Invention
The present invention relates to imaging apparatus such as light detecting apparatus, radiation detecting apparatus, etc. used in medical diagnostic imaging apparatus, nondestructive inspection apparatus, analyzing apparatus using radiation, and so on.
2. Related Background Art
FIG. 8 shows an example of an equivalent circuit diagram of an imaging apparatus applied to the radiation detecting apparatus, and FIG. 9 a plan view thereof. In FIGS. 8 and 9, P11 to P44 designate photoelectric conversion elements, and T11 to T44 TFTs. The photoelectric conversion elements are connected to common bias lines Vs1 to Vs4, and a constant bias is applied to them. A gate electrode of each TFT is connected to a common gate line Vg1 to Vg4. Each gate line is connected to a gate drive device and on/off of the TFTs is controlled by drive pulses from the gate drive device. A source or drain electrode of each TFT is connected to a common signal line Sig1 to Sig4 and the signal lines Sig1 to Sig4 are connected to a read device.
X-rays irradiated toward an object are attenuated and transmitted by the object, the transmitted X-rays are converted into visible light in a phosphor layer, and this visible light enters the photoelectric conversion elements to generate charges in the respective photoelectric conversion elements. The charges are transferred through the TFTs into the signal lines by gate drive pulses applied by the gate drive device to be read by the read device. Thereafter, the charges generated in the photoelectric conversion elements are removed by the common bias lines Vs1 to Vs4.
A typical example of the conventional radiation detecting apparatus of this type is a radiation detecting device in which the foregoing phosphor layer is bonded to the imaging apparatus of MIS-TFT structure comprised of MIS photoelectric conversion elements and switching TFTs.
FIG. 10 shows an example of a schematic sectional view of the device. Numeral 10 denotes a photoelectric conversion element and 20 a TFT. Numeral 11 designates a lower electrode of the photoelectric conversion element; 12 insulating layers; 15 a bias line for applying a bias to the photoelectric conversion element 10; 16 a photoelectric conversion layer of the photoelectric conversion element 10 and a semiconductor layer of the TFT 20; 17 a wire formed on the semiconductor layer 16 and electrode layers for establishment of ohmic contact of the semiconductor layer 16; 21 a gate electrode of the TFT 20; 22 source and drain electrodes of the TFT 20; 30 a phosphor layer for conversion of incoming radiation into visible light; 31 an adhesive layer for adhesion of the phosphor layer 30; 32 a mounting protective layer; and 36 a moisture-resistant protective layer. The radiation is incident from above in FIG. 10 to be converted into visible light by the phosphor, and the visible light enters the MIS photoelectric conversion element to be converted into a charge to be stored.
In the radiation imaging apparatus of this structure, there were increasing demands for achievement of higher sensitivity for the purpose of reducing radiation doses and other purposes, while the incoming visible light was reflected by the protective films and others, so as to cause optical losses, posing a significant issue in the achievement of higher sensitivity. Particularly, in the case where there are provided a plurality of protective films having their respective separate functions, the foregoing issue can be serious in particular.
An object of the present invention is, therefore, to provide imaging apparatus and radiation detecting apparatus with high sensitivity on the basis of improvement in a configuration of protective films and others on the photoelectric conversion element to reduce the reflection caused by the films above the photoelectric conversion layer, in order to guide the light emission from the phosphor into the photoelectric conversion element efficiently.
In order to achieve the above object, an imaging apparatus according to the present invention is an imaging apparatus comprising a photoelectric conversion layer for converting incident light into charge, on an insulating substrate, an electrode layer formed on the photoelectric conversion layer, and a protective layer formed on the electrode layer, wherein relations of naxe2x88x92nbxe2x89xa61.5 and nbxe2x88x92ncxe2x89xa61.5 are met where na is a refractive index of the photoelectric conversion layer, nb a refractive index of the electrode layer, and nc a refractive index of the protective layer.
Another imaging apparatus according to the present invention is an imaging apparatus comprising a photoelectric conversion layer for converting incident light into charge, on an insulating substrate, an electrode layer formed on the photoelectric conversion layer, and a plurality of protective layers formed on the electrode layer, wherein relations of naxe2x88x92nbxe2x89xa61.5 and nbxe2x88x92nc1xe2x89xa61.5 and nc1xe2x88x92nc2xe2x89xa61.5, . . . , and ncixe2x88x92nci+1xe2x89xa61.5 are met where na is a refractive index of the photoelectric conversion layer, nb a refractive index of the electrode layer, and nc1, nc2, . . . , nci, and nci+1 (i=1, 2, 3 . . . ) are refractive indices of the protective layers in order from the side adjacent to the electrode layer.
The details will be described in the embodiments of the invention.